1. The Field of the Invention
The present invention relates to neutral glass having high hydrolytic stability and a low proportion of boron oxide, its production and use.
2. The Description of the Related Art
Boron oxide is known to be teratogenic. This fact has relevance, in particular in the process of producing glasses, because with the use of boron oxide laborious occupational-safety measures are necessary which increase the production costs of the product. Further, boron components which are leached out of the glass may have toxicologically critical effects on living beings.
Due to its otherwise extremely advantageous properties, in particular with respect to chemical and physical resistance, borosilicate glass is often used in primary pharmaceutical packaging, for example in ampoules and syringes.
It is desirable to have glasses which on the one hand have the excellent properties, in particular with respect to hydrolytic stability, of borosilicate glasses and on the other hand have a low content of boron oxide.
In this case it is further desirable that the processing temperature is low so that the production costs are low.
In prior art (e.g. U.S. Pat. No. 7,144,835 B2) the processing temperature of glasses having high stability is reduced by the addition of a relatively large amount of boron oxide which replaces one part of SiO2 in the glass. Thus glasses can be produced which have excellent stability with a good processing temperature. However this concept cannot be used any longer due to the discovery of the harmfulness of boron oxide. If instead of boron oxide more SiO2 is used, the low melting temperatures cannot be achieved any longer.
A similar strategy is also used in DE 44 30 710 C1. In this case the inventors tried to lower the content of boron oxide and increase the proportions of other components, such as Al2O3 and SiO2. The result is a glass having a middle-rate processing temperature which only has good hydrolytic stability if it contains more than 8% by weight of boron oxide.